Silk Fibroin Bending Actuators as an Approach Toward Natural Polymer Based Active Materials

This work reports on the development of ionic liquid (IL)/silk fibroin (SF) composite films as electroactive polymers actuators. Different contents (20, 40, and 60% wt) of 1-butyl-3-methylimidazolium tricyanomethanide ([Bmim][C(CN3)]) and choline dihydrogen phosphate ([Ch][DHP]) ILs were incorporated into the SF polymer matrix. Due to IL–SF interactions, morphological changes such as globule-like nanostructures are induced in the samples. High concentrations of IL promote SF β-sheet formation above 65%. Further, an increase in the thermal stability of the SF was observed through the incorporation of [Bmim][C(CN3)]. IL type and content allow tuning of the electrical response as well as achieving bending actuation. [Bmim][C(CN3)]/SF samples allow bending responses up to 0.5 at an applied voltage of 3 V. In conclusion, this work demonstrates the ability of IL/SF composites to act as electroactive polymer actuators and opens new perspectives in the application of natural resources for smart materials.